Several forms of hereditary lung disease are being used to help understand the structure and function of normal lung. Patients with hereditary disorders of connective tissue are being evaluated by pulmonary function testing to make inferences of the mechanical-biochemical correlates of lung structure and function. The homozygous form of 1-antitrypsin deficiency associated with emphysema is being used to evaluate the role of antiproteases in protection of lung disease. Studies with a new drug, Danazol, has shown that 1-antitrypsin levels in these patients can be increased by 50%. Familial fibrotic lung disease is being evaluated as a model to understand the genetics of idiopathic pulmonary fibrosis. The homozygous forms of sickle cell disease is being used as a model to evaluate the effect of manipulation of the oxygen hemoglobin-dissociation curve on exercise tolerance. Fabry's disease is being evaluated as a model for the effect of inherent abnormalities of airway cells on the development of obstructive lung disease.